The drinks come in flashy cans and bottles with names like Red Bull and Adrenaline Rush. They don't taste great by almost universal consensus, but they're the fastest-growing segment of the beverage market because they deliver a quick punch of energy.

''A couple of years ago they were sort of an underground drink, served only at clubs. Pretty soon they're going to be everywhere,'' said Max Rodriguez, a marketing manager for the Edge Co., which imports Atomic Energy Drink from Brazil. ''They enable you to practically stay up all night and not get really drunk.''

The energy kick is delivered by a cocktail of stimulants. Many of the drinks contain caffeine and guarana, a South American plant used as a stimulant, plus a long list of herbs and vitamins promising better health and athletic performance.

''They definitely deliver a buzz or a jolt,'' said John Sicher, editor and publisher of Beverage Digest. ''They're generally party drinks. A very large percentage are consumed in bars or restaurants and used as mixers.''

Brent Isbell, 30, of Anniston, Ala. mixes energy drinks with alcohol to make cocktails. ''It gets you drunker quicker, if you can stand the taste of it,'' he said.

At Cosmopolitan, a trendy midtown Atlanta bar, bartender Chris Bates once served 400 Red Bull-and-vodkas in a night. The slim silver-and-blue cans are stacked behind the bar alongside the bourbon and rum, and Bates described Red Bull as ''absolutely the most popular thing we have.''

''We go through them like you wouldn't believe,'' he said. ''People want to get drunk and stay awake, and this pretty much does both.''

The drinks are so popular that beverage giants Coca-Cola Co., Anheuser-Busch, Pepsi Cola and Cadbury Schweppes have all rolled out their own energy drinks in recent months or plan to launch them soon.

The drinks first showed up in nightclubs in New York and Los Angeles and were favored by revelers who like to drink and dance till dawn. They spread to bars nationwide and are sold in liquor and grocery stores. Most cost about $2 for 8 ounces.

Fans say the drinks help them guzzle alcohol without passing out at the table. But dietitians warn that fatigue is the body's way of saying it's had enough to drink and that energy mixers may fool people into thinking they're not as drunk as they are.

''What you'll be is a wide-awake drunk,'' said Chris Rosenbloom, head of the nutrition department at Georgia State University. ''It's dangerous, this false notion that if I take this energy drink I'm alert and OK.''

Another dietitian, Cynthia Sass of the University of South Florida, said several stimulants, when put together can amplify each other and become dangerous. And, she cautioned, a long list of herbs and vitamins don't make a product healthy.

''They think if it's natural, then the more the better. That's not true,'' Sass said.